1. Technical Field
The present invention relates to a printer having a platen gap adjustment mechanism to adjust a gap between a printhead and a platen.
2. Related Art
Printers such as inkjet printers commonly have a platen gap adjustment mechanism to adjust a gap between a nozzle face of an inkjet head and a platen, or a gap between the nozzle face and a printing surface of a print medium conveyed over the platen. The platen gap adjustment mechanism adjusts the gap between the nozzle face and the platen, or the gap between the nozzle face and the printing surface of the print medium, in response to a control signal from a host device or a control unit inside the printer based on specifications of the print medium (such as its thickness and surface condition) and the state of the printer (such as errors).
JP-A-2005-280206 and JP-A-2005-280209 disclose printers having this type of platen gap adjustment mechanism. In the printers disclosed in these patent documents, a carriage carrying a printhead is supported by two carriage guide rails. The two carriage guide rails are attached to an elevator frame. The elevator frame is attached to move vertically on printer side frames located on opposite ends of the carriage guide rails.
The platen gap adjustment mechanism transfers rotation of an elevator motor attached to the printer frame through a geared transfer mechanism to one of the carriage guide rails. Rotation transferred to the carriage guide rail is then transferred through a gear train of multiple spur gears on the elevator frame to the other carriage guide rail. At the end of each carriage guide rail is a cam mechanism that changes rotational movement of the carriage guide rails to vertical movement of the carriage guide rails. The carriage guide rails move vertically in a synchronous manner by means of a rotary cam conversion mechanism. When the carriage guide rails synchronously move vertically, the gap between the recording head on the carriage and the platen on the stationary side changes.
JP-A-2005-280206 describes a mechanism for transferring rotation from one carriage guide rail to the other carriage guide rail. The mechanism uses a timing belt mounted on the two carriage guide rails in addition to a gear train of plural spur gears, and a connecting rod between rotary disks attached to the ends of the two carriage guide rails.
Although effective, platen gap adjustment mechanisms according to the related art still have issues that require resolution. For example, six issues related to prior art platen gap adjustment mechanisms that need to be resolved are described below.
First, a synchronous rotary mechanism that connects and synchronously turns two carriage guide rails through a gear train of spur gears requires plural spur gears between the two carriage guide rails. The number of gears in the synchronous rotary mechanism increases as the distance between the rails increases, and the size of the elevator frame to which these parts are disposed also increases. Furthermore, because rotation of the elevator motor shaft must be transferred through a speed reducer, more spur gears are required to achieve the desired speed reduction. The space required to install the synchronous rotary mechanism therefore further increases.
Because space for locating the timing belt connecting the two rails must also be provided in a mechanism that uses a timing belt, the required installation space increases further when the gap between the rails is large. A mechanism having a connecting rod between rotating disks disposed to two rails likewise requires sufficient space for the connecting rods to move in conjunction with the rotating disks, and the required installation space increases accordingly.
Second, because there is backlash between the meshing teeth in a synchronous rotary mechanism using spur gears, both carriage guide rails cannot be synchronously driven with good precision due to backlash when transferring rotation starts and when the direction of rotation changes. If both carriage guide rails do not turn synchronously, variation can also occur in how far the carriage guide rails move vertically in conjunction with rail rotation. The platen gap can therefore differ between the one carriage guide rail and the other carriage guide rail.
Various problems can also arise in a mechanism using a timing belt due to backlash between the teeth of the timing belt and the gears on which the timing belt is mounted. Problems can also result in a mechanism connecting rotating disks with connecting rods due to backlash in the coupling between the rotating disk and the connecting rod.
To avoid such backlash in the synchronous drive mechanism, play (a dead zone) of specific size must be provided in the cam mechanism that converts shaft rotation to vertical movement of each shaft. This configuration can move the rails vertically and adjust the platen gap with good precision after eliminating backlash between the gears and starting synchronous rotation in the synchronous rotary mechanism when the rails start turning and when the rails change direction. However, providing a specific play in the rotary cam increases the diameter of the rotary cam and increases the space occupied by the cam mechanism.
Third, in the platen gap adjustment mechanism according to the related art, rotation of the shaft of the stationary elevator motor attached to the printer frame is transferred through a geared transfer mechanism to a carriage guide rail on the elevator mechanism side. The spur gear on the stationary side and the spur gear on the elevator side remained meshed in this geared transfer mechanism. Because the gears on the stationary and elevator sides must remain meshed, vertical movement of the gears on the elevator side cannot be increased. Increasing adjustment of the platen gap is therefore difficult.
Fourth, a geared transfer mechanism comprises plural spur gears that rotate on an axis parallel to the axis of the carriage guide rail. When torque from the stationary elevator motor is transferred to the gear fixed coaxially to the carriage guide rail, force is applied to this gear in the direction of rotation from the drive-side gear. Force therefore works in the direction causing the carriage guide rail to move vertically. To prevent this force from causing the carriage guide rail to move vertically, a spring member that can produce a strong spring force must be provided to prevent the carriage guide rail from moving. Because a strong spring force is thus applied, the durability of the gears and parts supporting the carriage guide rails decreases, and space for accommodating a large spring member is required.
Fifth, with the platen gap adjustment mechanism according to the related art, rotation of the stationary elevator motor affixed to the printer frame is transferred through a geared transfer mechanism composed of spur gears to the carriage guide rails on the elevator side (moving side). With a geared transfer mechanism, spur gears on the stationary side and spur gears on the moving side must be kept meshed. Because the gears on the stationary and moving sides cannot disengage, the spur gears on the moving side cannot move very much up and down. Increasing the platen gap adjustment distance is therefore difficult. The gears on the rotating side and the gears on the elevator side also cannot be offset in the direction of the gear width (along the axis of rotation). Parts on the stationary drive source side, and parts on the vertically moving side can therefore not be offset greatly in the tooth width direction, and the layout is therefore limited.
Sixth, conveyance rollers for conveying the print medium past the platen are disposed in the printer on the upstream and downstream sides of the platen in the conveyance direction. The conveyance rollers are disposed across the width of the print medium conveyance path between the printer side frames. Parts of the media conveyance power transfer mechanism that transfers rotation to the conveyance rollers are disposed on the outside of one side frame of the printer. Providing space for the platen gap adjustment mechanism on the same printer side frame as the power transfer mechanism is therefore difficult. The platen gap adjustment mechanism must therefore be disposed to the printer side frame on the opposite side of the printer, and freedom in locating the platen gap adjustment mechanism is therefore limited.